update save version check

Author: moritz-h

src/GameTypes/Save/SaveHeader.cpp

@@ -13,8 +13,9 @@ void Satisfactory3DMap::SaveHeader::serialize(Satisfactory3DMap::Archive& ar) {
         throw std::runtime_error("Unknown Save-Header Version: " + std::to_string(save_header_version_));
     }
     ar << save_version_;
-    if (save_version_ != 29) {
-        throw std::runtime_error("Unknown Save Version: " + std::to_string(save_version_));
+    if (save_version_ < 29) {
+        throw std::runtime_error(
+            "Save version must be at least 29 (Update 6). Found old version: " + std::to_string(save_version_));
     }
     ar << build_version_;
     ar << map_name_;